The invention relates to a method of manufacturing non-slip floor coverings made of mineral materials, such as, for example, natural stone, fine stoneware, artificial stone or ceramics.
A special area of application for the invention is to increase or produce an anti-slip effect on highly polished floors, especially those used in public buildings or in buildings accessible to the public, as well as in those areas where liquids of every kind can land on the floor.
Slipping is one of the most frequent causes of accidents in Germany. The severity of such accidents is usually underestimated. To increase safety underfoot, shoe-soles and floors must be designed to be anti-slip. This is necessary above all where media which encourage slipping land on the floor. In many areas of public life, but also in the private domain, it is usual to use polished, shiny natural stone and artificial stone slabs as typical floor coverings both in dry and wet areas and in transitional areas. What is important here is to bring the anti-slip characteristics into harmony with the architectonic aesthetics. The evaluation of the anti-slip effect takes place according to DIN 51097xe2x80x94(Determining the anti-slip propertyxe2x80x94barefoot regions subject to wetnessxe2x80x94inspection proceduresxe2x80x94inclined plane) and DIN 51130 (Determining the anti-slip propertyxe2x80x94workrooms and work areas with increased danger of slippingxe2x80x94inspection proceduresxe2x80x94inclined plane) by means of an inclined plane.
However, there also exist measuring implements for the non-stationary measurement of the coefficient of friction. [Fb 701 Comparative study of the non-stationary measurement of the coefficient of friction on floors (Schriftenreihe der Bundesanstalt fxc3xcr Arbeitschutz)].
There exist different methods of producing or increasing the anti-slip properties of floors made of natural or artificial stone. The use of these methods is predominantly dependent on where the floor covering is to be laid or is already laid (inside area, outside area, degree of soiling to be expected, amongst other things). The most important methods will be briefly described below.
In abrasive blasting, abrasive-blasting materials corresponding to the desired roughness are hurled against the surface at high pressure. The more or less hard abrasive-blasting material leads to irregular roughening and severe dulling of the surface (DE 31 39 427).
In flame-blasting, high-energy fuel-gas oxygen flames are produced with which the surface to be treated is briefly heated. Through the action of the flames, there is a bursting of the quartz in the uppermost region of the stone as well as melting of stone portions which then solidify like glass and adhere to the surface relatively loosely (DE 35 45 064).
The granulation takes place with the use of a granulating tool (granulating hammer) which is provided with a plurality of evenly arranged chisel points. During a continuous movement of the workpiece, the granulating hammer is struck against the surface with a certain frequency (DE 39 33 843).
The described, or similar, methods which use abrasive means or chisel-like tools, admittedly lead to an increase in safety underfoot, but, like other surfaces, for instance those which are less polished during manufacture, also to a considerable loss of brightness and thus a reduction in their aesthetic appeal.
The coating of surfaces in order to increase their non-slip quality has the consequence that the treated surface is provided with burls (DE 33 42 266). This method does not admittedly bring with it any alteration of the visual characteristics but is only of limited durability since it is not possible to avoid abrasion.
In the chemical etching treatment of natural stone surfaces, above all the feldspar portions are attacked by the effect of substances containing hydrofluoric acid. (Informationsblatt des Bundesverbandes Trittsicherheit, Abteilung xc3x96ffentlichkeitsarbeit). The damage only amounts to a few micrometers, the quartz is largely spared. The loss of brightness depends on the length of the action; the alteration of the whole appearance must be tested on a sample surface.
However, this method is largely limited to being applied to mineral floor coverings. Chemical composition and concentration must be adapted to the different types of coverings. Because of the long reaction times and the necessity of keeping to the exact concentration, this method cannot be integrated into the process of manufacturing floor slabs or flags, or only with very high outlay. Where there is inappropriate application and disposal of the substance containing hydrofluoric acid, there is an increased risk to workers"" safety and the conservation of the environment.
In DE 195 18 270 or WO 96/36469, a non-slip floor covering and a method of manufacturing same are likewise described, the anti-slip effect being achieved here in that a dense net of microcraters, which are supposed to be invisible to the human eye, is produced on the surface of the floor covering, preferably polished slabs of natural stone or fine stoneware, by means of laser irradiation. This solution represents a clear improvement on the preceding state of the art.
An increase in the anti-slip effect, however, such as is desirable, e.g. in certain wet areas, can admittedly be achieved with laser irradiation by increasing the density of the craters and enlarging the lateral extension and the depth of the craters.
What is disadvantageous here, however, is that there can then be clear impairment of the visual characteristics, or a loss of brightness. A further disadvantage is that an increase in crater density and dimensions is connected with a lowering of the process speed. Often the peak pulse power achievable with a conventional pulsed laser is not sufficient to increase the crater dimensions.
Thus, the object of the invention is to propose a method of manufacturing non-slip floor coverings. with the aid of which method an increase in the anti-slip effect can be achieved without there being any disadvantageous impairment of the typical surface characteristics on the one hand and without any lowering of the process speed occurring, and in which, moreover, all the advantages of the laser structuring over other methods of providing an anti-slip surface are retained.
According to the invention, this object is achieved with a method as disclosed hereafter.
It is essential here that the non-slip floor covering, obtained in known fashion as per DE 195 18 270 or WO 96/36469 is subjected to continuous hydromechanical aftertreatment. This hydromechanical aftertreatment can preferably take place in the same installation directly following the laser treatment and retaining the same process speed, whereby the whole process, which comprises two process stages (laser treatment and hydromechanical aftertreatment), can be carried out continuously.
In certain cases however, e.g. when laser-treated floor coverings only receive the hydromechanical aftertreatment at the place of installation, it can also be propitious for the two process stages to run separately, i.e. not continuously.
Advantageous developments of this whole process are represented hereinafter.
In accordance with the method according to the invention, the laser-treated surface of the floor coverings or slabs conveyed horizontally are briefly sprayed at least once with an acid, preferably slightly acid, liquid during the continuous advance of the slabs.
After each of these spraying operations, the spray liquid is preferably distributed by means of brushes or a wiper blade evenly on the surface of the floor coverings or slags and superfluous spray liquid is removed.
This even distribution preferably comes about in such a way that the spray liquid only remains in the depressions and in the microcraters produced by the laser treatment, but not on the polished surface of the floor coverings or slabs. Here the dosage of the liquid is chosen to be an amount corresponding approximately to the volume of the depressions and microcraters.
As a result of the effect of the laser, the surface of the craters is microscopically very rough and thus very large in relation to the volume of the craters. This produces very good conditions in which the dilute acid can work in the craters produced by the laser treatment and in the micropores which, depending on the type of slab, are present despite the polish. The pH-value and the reaction time of the substantially diluted acids by comparison with the chemical engineering treatment of floor coverings are selected according to the invention to be such that the polished surface is not impaired yet, inside the craters, because of the good reaction conditions, parts of the surface are etched and thus there is an increase in volume. By preference, those craters which are located in the region of the feldspar portions of the natural stone or fine stoneware slabs are enlarged.
It is important to mention at this point that the reaction of time of the acid spray liquid depends on many factors, especially
the process speed
the distance between the first and the last of the spraying operations serving to cleanse the surface from any preceding spray operations and
the concentration of the acid.
What is important is that the acid, which in individual types of application can also be concentrated, only affects the depressions and microcraters without any impairment of the rest of the polished surface.
After the hydromechanical processing and the subsequent short (lasting preferably between 60 and 150 s) reaction time of the acid in the craters, the slabs are then sprayed again with a liquid, here at the highest possible pressure, and brushed once more. Corresponding to the pH-value of the first liquid, the liquid to neutralise completely can be water or also slightly basic (for example diluted lye).
In this connection, an advantageous development can consist of the fact that the pH-value of the liquid running off can be determined continuously and this value used as the regulating variable for the pH-value of the spray liquid.
Through the mechanically stronger effect of the brushes in relation to the distribution of the acid, residues which no longer belong to the particle bond of the mineral components of the floor slabs and which would otherwise lead to a decrease in the possible crater volume, are removed from the craters at the same time.
After the washing or neutralisation process, the slabs are dried with hot air.
The big advantage of the method according to the invention consists in fact that, using this method, the advantages of the laser-structured floor coverings and slabs are preserved and the anti-slip effect is noticeably increased.